The sensory nervous system is a common target for genetic diseases, metabolic disorders, and traumatic injuries. It has recently been shown that a cascade of transcription factors controls development of vertebrate sensory nervous system. Among these, POU domain factor Brn-3a regulates expression of genes that are important for sensory neuron survival, phenotypic differentiation, and axon path finding. Although Brn-3a is present in almost all precursors in the sensory ganglia, loss of Brn-3a leads to specific down-regulation of neurotrophin receptors and cell death in sensory neurons, suggesting that additional factors may modulate Brn-3a functions during sensory neuron development. Using the yeast two-hybrid screen, we have identified a novel nuclear kinase, homeodomain protein kinase 2 (HIPK2) that interacts with the POU homeodomain of Brn-3a, enhances Brn-3a-DNA interactions, and modulates Bm-3a-mediated gene expression. Based on these data, we hypothesize that HIPK2 is a transcription cofactor that regulates Brn-3a functions at different stages of sensory neuron development. However, because of its ability to interact with other homeodomain proteins, HIPK2 may also regulate neuronal functions via Bm-3a-independent pathways. The main objective of the proposed study is to investigate the mechanisms by which HIPK2 regulates sensory neuron functions. We propose the following specific aims to achieve this goal. Aim 1: To characterize the-nature of Bm-3a-HIPK2 interaction and to demonstrate such interactions during different stages of sensory neurogenesis. Aim 2: To determine if HIPK2 can modulate Brn-3a functions by phosphorylation. Aim 3: To characterize the roles of HIPK2 in regulating gene expression, survival, and axon path finding in sensory and sympathetic neurons. Aim 4: To investigate the mechanisms that regulates the distribution of HIPK2 during sensory neuron differentiation. Understanding the molecular mechanisms that regulate Brn-3a and HIPK2 functions will lead to important insights regarding the control of survival, differentiation and axon path finding of sensory neurons during development, injury, and regeneration. The interdisciplinary nature of this research program necessitates the central involvement of the PI in training students and postdoctoral fellows in the research areas in which they are inexperienced. The funding of this proposal would enable the PI to devote much of his efforts to research and significantly enhance the ability of the PI to accomplish his goals in research by reducing his clinical, teaching and administrative duties.